Embedded microstrip interconnection lines for gigahertz digital circuits

Transmission line structures are needed for the high-performance interconne ction lines of GHz integrated circuits (IC's) and multichip modules (MCM's) , to minimize undesired electromagnetic wave phenomena and, therefore, to m aximize the transmission bandwidth of the interconnection lines. In additio n, correct and simple models of the interconnection lines are required for the efficient design and analysis of the circuits containing the interconne ction lines. In this paper, we present electrical comparisons of three tran smission line structures: conventional metal-insulator-semiconductor (MIS) and the embedded microstrip structures embedded microstrip (EM) and inverte d embedded microstrip (IEM). In addition, we propose closed-form expression s for the embedded microstrip structures EM and IEM and validate the expres sions by comparing with empirical results based on S-parameter measurements and subsequent microwave network analysis. Test devices were fabricated using a 1-poly and 3-metal 0.6 mu m Si process . The test devices contained the conventional MIS and the two embedded micr ostrip structures of different sizes. The embedded microstrip structures we re shown to carry GHz digital signals with less loss and less dispersion th an the conventional MIS line structures. S-parameter measurements of the te st devices showed that the embedded microstrip structures could support the quasi-TEM mode propagation at frequencies above 2 GHz. On the other hand, the conventional MIS structure showed slow-wave mode propagation up to 20 G Hz. More than 3-dB/mm difference of signal attenuation was observed between the embedded microstrip structures and the conventional MIS structure at 2 0 GHz. Finally, analytical RLCG transmission line models were developed and shown to agree well with the empirical models deduced from S-parameter mea surements.